Soft contact lenses are generally prepared from certain hydrophilic polymers. The first soft contact lenses marketed were composed of hydroxyethyl methacrylate (HEMA). Today some lenses feature HEMA cross-linked with ethylene glycol dimethacrylate (EDMA), while others are formed of a polymer obtained by polymerizing a mixture of HEMA, EDMA, methacrylic acid and poly (N-vinylpyrrolidone) (PVP). Such lenses exhibit marked hydrophilic properties and when wet are soft and flexible.
While the present invention is useful for both hard and soft contact lenses, the following discussion will focus primarily on the special needs and qualities of soft contact lenses. The primary difference between conventional hard contact lenses and soft lenses is the polar or water attracting character of the hydrophilic gel material from which soft lenses are made. It is this property that gives soft contact lenses their unique physical properties and clinical behavior. This polar or water attracting character of the gel material is caused in part by the presence of hydroxyl groups (--OH) which attract and hold large amounts of water. The high water content of the expanded polymeric matrix results in special difficulties in the cleaning and disinfecting of soft contact lenses. The hydrophilic nature of soft contact lenses makes them especially vulnerable to bacterial contamination.
While studies have demonstrated that bacteria cannot penetrate the intramolecular pores of the hydrophilic polymer, the bacteria have an affinity for the protein and tear deposits on the surfaces of the lens itself. In particular, the compounds and fluid absorbed by the soft lenses provide an excellent bacterial culture media.
Similarly, any residual protein deposits from tear secretions remaining in or on the lens will readily inactivate the most effective germicidal components of a disinfecting system. These organic residues serve as a growth media for a variety of potentially harmful micro-organisms. Thus, in cleaning soft contact lenses, it is important to remove substantially all of the physiological deposits, (i.e. mucins, lipids, and proteins contained in tears and exudates) which are attracted to and build up on the surfaces of the lenses.
In order for soft contact lenses to be effectively cleaned, it is important that all contaminants be removed from both the surfaces and the interior of the lens. Ordinarily, contact lenses are removed each evening and are then reinserted into the eyes upon awakening. The period of removal provides an opportunity to disinfect the lenses by their placement in an antiseptic solution, typically one which contains hydrogen peroxide, although other disinfectants such as chlorhexidine are known and may be used. Hydrogen peroxide permeates a soft contact lens, oxidizes the protein that is present on the surface of the lens and is simultaneously an effective sterilant for any micro-organisms that are present.
The effectiveness of hydrogen peroxide (H.sub.2 O.sub.2) is well known. However, prolonged exposure to hydrogen peroxide typically causes soft lenses to distort, thereby rendering them unsafe. Furthermore, residual hydrogen peroxide remains following cleaning of the contact lenses and results in eye irritation since hydrogen peroxide is a strong eye irritant. The problem is exacerbated in soft contact lenses, since the hydrogen peroxide can be absorbed into the hydrophilic lens. Thus, when the contact lens is placed on the eye, the hydrogen peroxide is released to irritate and/or harm the sensitive tissues of the conjunctivae or cornea. It is therefore necessary to remove or neutralize any residual hydrogen peroxide both on and in the soft contact lens prior to use.
The instability of hydrogen peroxide solutions is well known as it decomposes into water and oxygen. Allowing a solution of H.sub.2 O.sub.2 to stand exposed to atmospheric conditions at ambient temperatures will eventually result in complete degradation of the hydrogen peroxide solution. However, the time necessary for complete degradation or neutralization to occur is typically on the order of several days. The prospect of being unable to use the contact lenses for several days presents the user with an intolerable situation.
In the past, when hydrogen peroxide has been utilized in contact lens disinfection regimens, various means have been proposed for the accelerated neutralization or decomposition of residual hydrogen peroxide. For example, it is known in the prior art to neutralize a disinfectant hydrogen peroxide solution through the use of chemical additives. U.S. Pat. No. 4,568,517 to Kaspar et al. discloses a contact lens disinfecting system wherein a chemical neutralizer, e.g. sodium sulfite or sodium thiosulfate is added to the disinfecting solution. U.S. Pat. No. 4,521,375 to Houlsby, teaches a sterilizing treatment with hydrogen peroxide and the neutralization of residual amounts thereof through the use of a chemical neutralizer consisting of sodium pyruvate. However, these methods result in the solution containing and the lenses being left in the presence of undesirable by-products of the chemical neutralization.
An effective solution to the neutralization problem has been found in the use of one or more catalysts to enhance the decomposition of the hydrogen peroxide solution. The use of catalytic agents to accelerate the neutralization of residual hydrogen peroxide absorbed by contact lenses in the course of sterilization is disclosed in U.S. Pat. No. 3,912,451 to Gaglia, Jr. This patent disclosed a method of removing hydrogen peroxide from soft contact lenses through the use of a metallic decomposition catalyst from Group IV-VI of the Period Table. Although Gaglia's method represents an improvement over the prior methods, specifically the ambient decomposition method, in that it substantially shortens the decomposition time, it still takes at least six hours to reduce the percentage of peroxide to an acceptable level for contact lens wear.
Often the catalyst is in the form of an enzyme as disclosed in U.S. Pat. No. 4,473,550 to Rosenbaum et al or in U.S. Pat. No. 4,826,658 to Kay. In both of these patents, the hydrogen peroxide is decomposed by an enzymatic reaction. However, the entire cleaning and disinfecting process disclosed in either patent requires multiple steps, with the wearer of the contact lenses being required to follow relatively specific instructions, which if disregarded could cause physical harm.
Another method for disinfecting contact lenses is disclosed in U.S. Pat. No. 4,202,740 to Stoner et al wherein electrolytically charged chloride ions are used as the disinfectant. In the method of Stoner et al, the device holding the contact lenses must be made of a conductive material in order to serve as a bipolar system whereby the ions flowing through the electrolyte decontaminate the contact lens. However, uneven current distribution throughout the solution will result in shadows and an incomplete disinfection. Further, the voltages must be kept below the potential at which electrolytic oxygen and chloride from the water and sodium chloride are generated.
Electrolysis of hydrogen peroxide as a means to neutralize the disinfectant solution is disclosed in U.S. Pat. No. 4,836,859 to Konishi et al. The aqueous hydrogen peroxide according to that invention contains a single salt such as sodium chloride. The Konishi solution contains a buffer and may even have an antiseptic added. However, the Konishi solution does not include a surfactant, it being well known that hydrogen peroxide is unable to retain its bactericidal properties in the presence of certain surfactants.
Adequate rinsing of the disinfected lenses poses additional problems since it requires a considerable amount of time and personal attention in order to carry out an adequate rinsing procedure. For an adequate soaking and rinsing sequence, it has been found that often four separate rinses are required, which may take a total of 30 minutes or more. Another drawback is the fact that rinsing procedures and sequences are highly subjective and lack reproducibility, such that they can vary widely in effectiveness from one person to another. Furthermore, large volumes of solution are necessary to carry out adequate rinses which over time makes the practice cumbersome and inconvenient. Still further, some rinse systems are confusing to patients, while others are expensive.
It is thus apparent that a need exists for an improved electrolytic cleaning and disinfecting solution which provides easy and effective cleaning and disinfection of contact lenses, particularly soft contact lenses. While the solution of this invention is particularly suited for disinfecting and cleaning of soft contact lenses, it is contemplated herein that the invention would be useful on any article or device that is suited for cleaning and disinfection via electrolysis.